There are over 100 North American species in 11 genera in the mayfly family Heptageniidae. They are found in lotic or lentic erosional habitats, often among rocks. They are sometimes collector-gatherers of fine organic particles; however, they typically feed by scraping algae and periphyton from rocks and other substrates at the bottom of the stream. They have a flattened head and body, which allows them to cling to the tops of the rocks, even in fast flowing water, without being swept away, or to squeeze among rocks. This flat body shape makes them great at clinging to surfaces, but fairly poor, floppy swimmers. The emerging duns (sub-adults) are important in the fly-fishing community, with several genera in the family serving as models for tied flies.